In relation to a spectrometer whose operation is influenced by the wavelength of light, the present invention specifically relates to a spectrometer with a location detecting device. More specifically, the invention relates to assigning the wavelength location of diffracted light which is diffracted by a wavelength dispersion, or scattering, element in the spectrometer.
For radiation dispersion, a reflection type diffraction grating (a main grating) with, more or less, 1800-4800 grooves or lines/mm is used. For a wavelength dispersion sub-element, a flat surface sub-diffraction grating with, more or less, 10-100 grooves or lines/mm is used. The sub-diffraction grating is securely connected to, and driven with, the main grating. The location detection of the main grating is the detection of the outgoing angular spread of dispersed light, and the detected dispersed wavelength is precisely assigned by a detector.
The light to be dispersed is admitted through an incident, or inlet, slit. The light admitted through the incident slit exits via an outlet slit after dispersion by the main grating, and is detected by a main detector. At this moment, the intensity of light at a selected wavelength can be measured by way of letting it pass through the outlet slit.
The sub-diffraction grating receives light with a narrow bandwidth (the light for detection) such as laser radiation for location detection. The light which is acted on by the sub-diffraction grating is admitted into a sub-detector having a multiple number of detection elements in line towards the dispersion direction after diffraction by the sub-diffraction grating. Since the number of grooves in the sub-diffraction grating is smaller than the number in the main grating, multiple degrees of diffraction light is diffracted by the sub-diffraction grating.
The interval between diffraction lines which are admitted into the sub-diffraction grating is determined by the driving position of the sub-detector, the number of grooves on the sub-diffraction grating, the wavelength of light source, the distance between the sub-diffraction grating and the sub-detector, etc. Since the diffraction lines traverse, one by one, the sub-detector as a result of the driving of the sub-diffraction grating, the location detection of the wavelength dispersion element with usage of the diffraction lines can be detected by way that the interval between diffraction lines and the width of the sub-detector are set, always with more than one diffraction line admitted onto the sub-detector and with the main diffraction grating and the sub-diffraction grating secured to, and driven concurrently with, each other.
The density of the detected lines is far larger than that of the dispersion lines.
Therefore, in case that a detected line can be detected by the main detector simultaneously, the detected light which is admitted into the main detector can create interference for the detection of light for detection.